Wikipedia possibly has the corrected birth date, but either you are confusing him with someone else or the memorial is wrong for his date of death.A quick check on the Westminster Abbey site gives a dead of death agreeing with that in the data, 7th Dec 1775.

Posted by Tony Willoughby on Friday 4th of August 2017 10:00

Wikipedia has his date of birth as 19.9.11 and his memorial in Westminster Abbe=y has his date of death as 21 November 1761